Track ballast usually consists of crushed rocks or stone, but in some cases, less suitable alternatives, like burnt clay, are also used.

轨道道砟通常由碎石或石头组成，但在某些情况下，也使用不太合适的替代品，如烧粘土。

And the old man touched the door with a ring of graved jasper and it opened, and they went down five steps of brass into a garden filled with black poppies and green jars of burnt clay.

老人用一只刻纹的碧玉戒指在小门上挨了一下，门就打开了，他们走下五级铜阶，来到了一个长满了黑色辖粟花的花园，那里有很多绿色的瓷瓦罐。